A well-known objective in the design and construction of crab traps, whether for king, snow, dungeness or other crab, is to provide an entryway into an enclosure which does not pose significant barriers or deterrents to the crab's entrance, but which also provides a significant barrier or deterrent to escape. Typically, this problem is addressed in one of two ways. The first is to provide an upwardly-sloped entry tunnel through which crabs will crawl seeking bait located inside the trap. Escape from the trap is prevented by spacing the interior end of the entry tunnel some distance above the bottom of the trap so that entering crabs spill over into the trap enclosure, unable to climb out. Examples of crab traps using this type of entry are shown in U.S. Pat. Nos. 3,184,881; 3,209,484; 3,300,890; 3,373,523; and 4,075,779. The second is to provide a swinging or deflectable gate at the opening which acts as a one-way door. Examples of this type of trap are shown in U.S. Pat. Nos. 2,530,449; 3,678,612; 4,184,283; and 4,887,382. Some of these traps incorporate a combination of these devices
A problem associated with the first approach is that once a quantity of crabs accumulates in the bottom portion of the trap, those which enter later are capable of reaching the inner edge of the entryway and escape outwardly therethrough. A problem associated with the second approach is that some crabs are deterred from entering by even slight physical interference or by the electrolytic charge which may build up between submersed moving metal parts.